1. Field of the Invention
The invention relates to a cable lug for connecting the end of a cable to a screw-type terminal, with a flat U-shaped contact fork that is open toward the front and merges into a fork shaft toward the rear, said fork shaft being provided with connecting means for the connection to a cable end, whereby at least one base plate configured as a signal conductor, and at least one damping disk made of elastic material with at least one cover plate, are assembled in a stacked, sandwich-like manner within the area of the contact fork.
2. The Prior Art
Such cable lugs are preferably employed as connection elements for electrical high-current connections for connecting the ends of cables to screw bolt-type connectors, the latter being referred to as screw or connection terminals. Such terminals are substantially formed by a threaded bolt that projects vertically from a contact surface, whereby a nut or another type of terminal element with a female thread can be screwed to the free end of said threaded bolt. For connecting the cable lug to such a terminal, the contact fork is first pushed into an axial gap between the contact surface and the nut and then radially onto the screw bolt, and the nut is subsequently tightened, so that the contact fork is axially solidly clamped between the nut and the contact surface of the terminal.
Due to the relatively large contact surfaces in the U-shaped zone of the contact fork, the transition resistance to the corresponding contact surfaces on the terminal is accordingly low. Such cable lugs are therefore frequently used for connecting loudspeaker cables with large conductor cross sections with high-load capacity, to the output terminals of amplifier output stages.
However, it has already been found that forming the contact fork from a simple sheet metal tab or plate is inadequate for such applications. Even if such a contact fork is solidly tightened by hand, it is possible that the contact fork is excited to mechanical vibrations by the sound frequency signals, which are transmitted with high current intensities, by magnetostriction, and also by body and air sound. Such vibrations lead to relative movements of the contact surfaces stacked one on top of the other, which is directly reflected by signal interferences. Such interferences are, of course, absolutely undesirable especially when connecting high-quality sound transformers to amplifier output stages.
In order to deal with the problems mentioned above, is has already been proposed in the prior art disclosed by U.S. Pat. No. 5,108,320, to realize the contact fork within the zone of the contact surfaces in the form of a sandwich-like construction comprising a base plate, an elastomer disk, as well as a cover plate. The base plate and the cover plate are realized in this connection as metal sheet forks congruently disposed on top of the other, with an also U-shaped rubber disk being clamped or glued in between said sheet metal forks within the zone of the U-shaped contact surfaces.
The contact surfaces clamped together in the connection terminal are elastically pressed against each other by the inherently elastic rubber or elastomer disk. The elastic initial clamping assures that the contact surfaces are pressed against each other in an elastic manner, which enhances the electrical transfer.
However, a basic problem in connection with the known cable lug lies in fixing the elastomer disk between the base plate and the cover plate in such a way that its optimal function is assured under all operating conditions, because it is necessary for such fixation that both shifting of the elastomer disk as a whole and any lateral squeezing out of the latter is effectively avoided when it is pressed axially. Gluing the disk to the cover or base plate would be considerably stressed by elastic deformations. Furthermore, the rubber would continue to swell out from between the cover and the base plates sideways, and the rubber material may be damaged by the wedge effect caused on the edges.
Furthermore, in connection with the known cable lugs, the elastomer disk is subjected to the risk that it may be crushed by the forces of pressure occurring in the terminal during clamping when the clamping nuts are tightened.
Finally, an added problem is that in the prior art, the elastomer disk is exclusively loaded spring-elastically in the axial direction, which means that it is possible that mechanical resonances may occur as a result of the undamped spring effect of the rubber material. This causes the contact surfaces of the contact fork and of the screw-type terminal to vibrate against each other without practically any damping.